A New Ignition Mechanism

  • If, throughout a GMC, the ambipolar diffusion time tAD were to instantaneously drop to a value less than the local free-fall time, the bomb would certainly ignite.

    How might this be accomplished?

  • Since tAD depends directly on the strength of the magnetic field, one might imagine a scenario by which the B-field inside the GMC decreases during a galaxy-galaxy interaction ... but you would be hard-pressed to find anyone who would buy such a scenario!

  • But it recently has dawned on us that,

    1. via the ionization rate zCR, the ambipolar diffusion time also depends on the flux of cosmic rays in the vicinity of the GMC, and

    2. from the "leaky box" model of cosmic-ray propagation, we know that the flux of cosmic rays is strongly concentrated toward the disk of the galaxy.

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